Gulf oil leak causing upheaval in marine ecology

As oil continues to leak out of the collapsed Deepwater Horizon well head, researchers are beginning to collect data on how it is changing life in the Gulf of Mexico.

Earlier today, Samantha Joye of the University of Georgia in Athens spoke of what they are finding. She said that methane concentrations in a giant underwater plume emanating from the well head are as much as 10,000 times higher than background levels. The consequences of this for life in the gulf are unknown.

Joye was one of the first scientists to discover deep-water plumes emanating from the ongoing spill and recently returned from a two-week research expedition on board the research vessel F. G. Walton Smith. "It's an infusion of oil and gas that has never been seen before, certainly not in human history," she said earlier today, as she described her preliminary findings.

The plume is more than 24 kilometres long, 8 kilometres wide and 90 metres thick, and stretches from 700 to 1300 metres below the surface south-south-west of the collapsed Deepwater Horizon well head.

Busy bacteria

Joye's team measured oxygen levels throughout the water column near the plume and found them to be lower than normal, all the way from the sea floor to the surface. She says this is a result of increased activity from bacteria that are digesting the oil.

The Gulf of Mexico is no stranger to decreased oxygen levels: every year, fertilisers pouring off the US coast boost algal growth, which sucks oxygen out of the water and stifles other life forms, creating one of the world's largest known dead zones.

Joye said she did not think the extra microbial activity would be significant enough to create additional dead zones in the gulf, because microbes need nutrients that do not exist in high enough concentrations at depth. But she cautions that the environmental implications are unknown.

"The system as a whole has been substantially perturbed by this event," says Joye. "When you interfere with the natural system, it's likely that problems will cascade up the food web."

No end in sight

One big unknown, she says, is how chemical dispersants that are being injected into the leaking oil to break it up will affect phytoplankton and other organisms at the bottom of the food chain. In fact, it's possible – but difficult to prove at this point – that the dispersants and oil are already killing phytoplankton, which could account for low oxygen levels recorded in near-surface waters.

And the oil and dispersants are likely to be around for a while yet: a seasonal change in surface current flows – from north-east to south-west – that takes effect in August means the mix will continue sloshing around the gulf rather than be pushed out into the open ocean.

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